The problem addressed by the present invention is that, during the winter, cross country truckers traditionally idle their engines during overnight rest stops to assure cold weather restart and to provide heat in the cab. In particular, to enable cold weather restart it is important to keep the truck's motor oil and diesel fuel warm. As is well known, motor oil provides proper engine lubrication only within a limited temperature range, and diesel fuel typically begins to wax at temperatures below 40 degrees Fahrenheit and becomes a virtually unusable gel at temperatures below 20 degrees Fahrenheit.
Idling the main truck engine overnight is one way to keep the truck's motor oil and diesel fuel warm and to thereby assure cold weather restart. This use of the main truck engine, however, is very inefficient. Typical truck engines, such as 300 to 500 BHP Diesel engines, are very inefficient when operated at 600 to 900 RPM at only 10 to 20 BHP -- i.e., the power level needed to idle the engine and to drive the truck's electrical generator, cab heater or air conditioner, and other cab accessories.
As provided by the present invention, one solution to the problem of maintaining a habitable environment in a truck cab overnight and keeping the engine warm so that it can be restarted after a cold winter's night, is to use a small cogeneration system which can perform these functions more efficiently than the truck's main engine. In particular, the cogeneration system includes a supplemental engine which supplies heat to certain engine components and also supplies power to a selected set of cab accessories which are normally powered by the main engine. Furthermore, the supplemental engine of the present invention can and preferably does use the same fuel supply as is used for the main truck engine.
The prior art includes a number of supplementary engine systems, often called pony engines, for use in trucks. See, for example, U.S. Pat. Nos. 4,682,649 (Greer, 1987) and 4,448,157 (Eckstein et al., 1984). However, the prior art pony engines have, generally, been too complicated, expensive and insufficiently energy efficient to achieve significant commercial success.
The present invention provides improved energy efficiency and reduced complexity by interconnecting the fluid coolant systems of the truck's primary and auxiliary engines, and using this interconnection as the sole mechanism for providing heat to the primary engine and the truck's cab and sleeper heaters.
The present invention also provides improved auxiliary air conditioning by providing an auxiliary condenser as well as an auxiliary compressor, and electrical controls for selectively enabling either the auxiliary or the primary compressor. The electrical control allow the auxiliary engine to drive the auxiliary compressor even when the primary engine is running, thereby allowing the air conditioning load to be removed from the primary engine.
It is therefore a primary object of the present invention to provide an improved auxiliary power system for trucks and other heavy duty vehicles.
Another object of the present invention is to provide a truck cogeneration system that uses waste heat from an auxiliary engine to heat the truck's main engine, cab and sleeper compartment.